Effect of C-type natriuretic peptide (CNP) on water channel aquaporin-4 (AQP4) expression in cultured astrocytes.

Astrocytes play a vital role in volume and ion control in the central nervous system. C-type natriuretic peptide (CNP) may be involved in neuronal-glial signaling, but its physiological role has not yet been characterized. In our study, we found that CNP can regulate the water channel aquaporin-4 (AQP4) expression in cultured astrocytes. Using immunocytochemistry and enzyme immunoassay, we found that primary neuronal cultures exhibited a high level of reactivity to CNP, and that cultured astrocytes exhibited reactivity to cyclic GMP after exposure of CNP. Using RT-PCR, immunoblot and immunocytochemistry, we detected increased levels of AQP4 mRNA and AQP4 immunoreactivity in the cultured astrocytes after they had been exposed to CNP or cyclic GMP. These results suggest that CNP, which is mainly produced by the neurons, effects the level of AQP4 in the astrocytes. Therefore, CNP may be a regulator of water homeostasis in the central nervous system.